Third Generation mobile communication technology (3G) generally refers to a new generation of a mobile communication system that integrates multimedia communications, such as integrating wireless communication and Internet-based communication. Such a mobile communication system is able to process various types of media data streams such as image, music, video streams and provide various information services such as web page browsing, teleconference, and e-commerce. With the development of the communication technology, people are setting more and more demanding requirements for the mobile communication. The network architecture and protocols of the existing 3rd Generation Partnership Project (3GPP) no longer satisfy users' high demand for mobile communication. Accordingly, 3GPP proposed a concept of an evolved network for fulfilling future communication requirements.
In particular, to ensure the competitive edge of the 3GPP in the further development, especially the capability of the 3GPP system for processing rapidly increasing IP (Internet protocol) data services, the 3GPP has launched a Long Term Evolution (LTE) program and a System Architecture Evolution (SAE) program. The purpose of the LTE is to provide an evolved communication network (such as an SAE network or a LTE network) which can reduce time delay, increase user data rate, enhance system capability and coverage, and save overall cost of operators of the network. Meanwhile, the backward compatibility of the evolved network structure toward the existing network is also an important factor to consider.
The evolved network structure meets the following requirements:
(1) a basic IP connection needs to be set up in the evolved network during an initial stage when a user equipment accesses the network;
(2) the evolved network structure must minimize the delay of the user data; and
(3) each function module in the evolved network architecture should be defined in such a way to avoid functional overlapping or repetition so as to avoid unnecessary signaling and time delay.
FIG. 1 illustrates a general network architecture derived from the above requirements. The network architecture mainly includes four logic function modules: a Mobility Management Entity (MME), a user plane entity (UPE) gateway (which is a Serving Gateways (S-GW) or an integrated gateway including a Serving GW and a PDN Gateway (P-GW)), an LTE Radio Access Network (LTE RAN), and a Home Subscriber Server (HSS). The MME is a mobility management module responsible for mobility management for a control plane. The mobility management includes management for user context and mobility state, assignment of information such as user temporary identity, mobility state, tracking area (TA), and verification of user identity. The MME corresponds to a control plane of a Serving GPRS Support Node (SGSN) in the Universal Mobile Telecommunications System (UMTS). The S-GW is responsible for initiating paging downstream data of a user equipment (UE) in an idle mode, managing and storing UE context, IP bearer parameters and routing information in the network, and managing UE's mobility control plane anchor and user plane anchor functions between the 3G and the SAE network. The S-GW corresponds to a data plane of SGSN in the current UMTS. The P-GW is responsible for a user anchor function that UE accesses the packet data network. The P-GW has packet routing and forwarding functions and is responsible for policy charging enhancement, packet filtering function based on each user, and is coupled to the S-GW to carry and deliver control information such as create/modify/delete. The LTE RAN is a radio access network for the evolved network. The nodes therein are not defined specifically. Generally, the LTE RAN includes an evolved base station (eNodeB), and may also include a control plane server (CPS) logic entity. In a logic sense, the LTE RAN can be treated as a Long Term Evolution Radio Access Network (LTE-RAN) entity.
Since network structures adopting different radio access technologies (RATs) may exist simultaneously in a real application, network registration procedures may be aroused in a “ping-pang” manner due to the change between different networks when the UE is moving between different RATs (e.g., between a conventional network (i.e. a 2G/3G network) and an evolution network such as an SAE network). As illustrated in FIG. 2, a Routing Area 1 (RA1) and a Routing Area 2 (RA2) are routing areas for an existing 2G/3G network. The UE of the existing 2G/3G network always initiates a Routing Area Update (RAU) procedure when switching a routing area (RA). Of course, even if UE does not switch RA, there is also a periodic location update procedure, the function of which is to inform the network that the UE is still in the network currently so as to prevent the network from keeping paging the UE without knowing that the UE leaves the network. A network registration procedure due to the movement of the UE is now illustrated below.
In FIG. 2, TA1, TA2, TA3, TA4 are tracking areas in the evolved network. TA is similar to RA in the 2G/3G network. When a multi-mode UE is moving between different RA and TA, to ensure that the UE can be paged in networks adopting different RATs, the UE needs to register with RA and TA that it enters. If the UE enters RA1, the UE needs to register with the SGSN of the 2G/3G network. When the UE enters TA1, the UE further needs to register with the MME of the evolved network. When the UE exits TA1 and re-enters RA1, the UE needs to register with the SGSN of the 2G/3G network again. However, the method results in frequent network registration procedures for ensuring paging, causing thereby considerable consumption of the registration signaling.
To solve this problem, various methods in conventional arts have been proposed to avoid frequent network registrations and a severe waste in the air-interfaces.
Currently, a schema for lessening the registration/update influence on air-interfaces is imposed by UE in the idle mode when entering networks with different RATs. The idea of the schema is that the UE registers with an access network (a 2G/3G network or an evolved network) after the UE attaches to the network. Then, the UE registers with another access network when the UE moves to the other access network. As such, the UE may register with both access networks. After that, when the UE moves between corresponding RAs or TAs of these two networks, the UE may not initiate any registration procedure. Both the access entities in these two access networks with which the UE registers contain corresponding UE context.
Now, the procedure of the UE first attaching to the SAE and then moving to the 2G/3G network is illustrated below.
As illustrated in FIG. 3, at step 301, the UE attaches to the SAE, sending an “attach request” message to the MME.
At step 302, the MME may acquire context from the HSS and initiate an authentication procedure with the UE.
At step 303, the UE returns an authentication response to the MME. If the authentication passes, it indicates that the UE has registered with the MME successfully. The MME assigns an SAE temporary mobile subscriber identity (S-TMSI)/SAE routing area (S-RA, i.e., TA) and a default IP address to the UE. The S-TMSI denotes a temporary mobile subscriber identity of the SAE network. The S-RA demotes the RA of the SAE, i.e., TA.
At steps 304 and 304′, the MME may register with the HSS (if the MME already contains the UE context, there is no need for the MME to acquire the context from the HSS).
At step 305, the MME confirms that the UE has attached to the network successfully and allows the UE to enter. The MME assigns a S-TMSI/S-RA to the UE and sends information of the default IP address to the UE.
At step 306, after the UE switches from a different RAT to the 2G/3G network, the UE initiates an RAU procedure and carries a S-TMSI/S-RA assigned by the MME to the SGSN (and may also carry parameters such as TMSI/RA assigned by the SGSN).
At steps 307 and 307′, the SGSN may send an SGSN Context Request message to an associated MME to request the UE context. After the MME receives the request message, the MME sends the associated context to the SGSN. Such procedure is referred to as a Context Retrieval procedure.
At step 308, authentication procedure may be performed. The SGSN may register with the HSS, as illustrated in steps 309 and 309′ (the SGSN may not register with HSS, but may treat the MME as the HSS).
At step 310, the SGSN confirms the receipt of the context and may trigger the MME to transfer data.
At step 311 and 311′, the SGSN may update Packet Data Protocol (PDP) context with the MME because the MME, at the user plane, is similar to an original GPRS Gateway Support Node (GGSN).
At step 312, the SGSN assigns U-TMSI (UMTS TMSI, Temporary Mobile Subscriber Identity of UMTS)/U-RA (Routing Area of UMTS) and S-TMSI/S-RA to the UE. After that, no update registration message needs to be sent when the UE moves between U-RA and S-RA. The U-TMSI denotes a temporary mobile subscriber identity of the 2G/3G network. U-RA demotes the RA of the 2G/3G network.
At step 313, the UE returns an RAU completion message.
The procedure that the UE first attaches to the 2G/3G network and then moves to the SAE network is similar to the procedure that the UE first attaches to the SAE network and then moves to the 2G/3G network as illustrated in FIG. 4, which will not be detailed herein.
Briefly, the UE first attaches to the SGSN. The SGSN registers with the HSS. Then, the UE enters the SAE network and initiates a RAU and retrieves context from the SGSN. The MME registers with the HSS and assigns a S-RA/S-TMSI to the UE. The UE does not need to initiate a location update/registration message when moving between the registered RA and S-RA (in terms of TA, RA, the UE may be assigned with a plurality of areas of the SAE network or the 2G/3G network, such as several S-RAs. Then, the UE does not need to initiate the update message when moving between the registered areas assigned by the networks). When the UE moves to areas beyond registered S-RA/RA, the UE needs to initiate an update message. It should be noted that if the SGSN is not replaced, the SGSN registration procedure may be unnecessary.
It is discovered that the above schema encounters at least the following issues in practical application. The network side may page the UE in an unnecessary paging area, reducing efficiency for paging the UE.
The root cause behind such problem is that in the current registration procedure, after the UE enters an RAT network, the UE performs registration and is assigned with TA/RA of the RAT network. After the UE enters another RAT network, the UE initiates an update procedure and is assigned with RA/TA of another RAT network. Then, the UE does not need to initiate the update procedure when moving between the registered RA and TA. When the UE enters a new RA or TA, the UE needs to initiate an update message. The SGSN/MME of the new RA/TA establishes an association with an access entity (MME/SGSN) of another RAT network. Accordingly, the UE does not need to initiate an update message when moving between the new RA/TA and the TA/RA assigned by the access entity of another RAT network.
As illustrated in FIG. 5, the TA is a registered area of the SAE network while RA is a registered area of the UMTS. According to the current schema, the UE registers with the MME when entering TA1 and initiates an UMTS location update after entering the RA1 and registers with the SGSN. Then, the UE does not need to initiate a location update procedure when moving between TA1 and RA1. As such, location update procedures due to ping-pang movement between two RAT networks can be saved. That is, the notion of the TA may help to avoid ping-pang update due to different TAs in one RAT.
After UE moves to RA2, the UE initiates a location update. Then, the UE does not need to initiate a location update procedure between TA1 and RA2 (when UE moves back to RA1, the UE still needs to initiate a location update. After that, the UE does not need to initiate a location update when moving between TA1 and RA1).
If the UE does not need to initiate a location update procedure when moving between TA1 and RA2, and the UE will initiate a location update procedure again when moving back from TA1 to TA2. After that, the UE does not need to initiate a location update procedure when moving between TA2 and RA2.
Likewise, when the UE moves to TA3, TA4 till TA5 again, the UE does not need to initiate a location update procedure when finally moving between TA5 and RA2.
However, it can be seen from the FIG. 5 that it is impossible for the UE to move directly between the TA5 and the RA2. In addition, the MME managing the TA5 may not be associated with the SGSN managing the RA2 (e.g., the MME and the SGSN belong to different Public Land Mobile Networks, and have no roaming interface, or due to distance reason, the “associable SGSN list” configured on the MME does not include SGSN which the RA2 belongs to). Therefore, a signaling procedure between the TA5 and the RA2 is not necessary. Since the UE can only enter an area around the TA5 in a next step and the UE is unlikely to enter the RA2, it is meaningless to associate the SGSN of the RA2 with the MME of the TA5. However, the RA2 still needs to be paged during a paging period, which may cause a mass of paging and reduce efficiency for paging the UE.
Alternatively, in practice, the UMTS is an all-covered network. The SAE is a network covering hot spots, as illustrated in FIG. 6. After UE registers with TA1 and RA1, the UE moves from RA1 to RA2 and to RA3. The UE does not need to initiate an update procedure when moving between TA1 and RA3. Alternatively, after UE registers with TA1 and RA1, the UE moves from TA1 to TA2 and to TA3 and to TA4. Then, the UE does not need to initiate an update procedure when moving between RA1 and TA4.
Usually, the area with which the UE registers (after registering with two different RAT networks) is referred to as UE registered area or non-update area. With no optimization such as priority residence, the paging area of the UE is the UE registered area (non-update area). However, actually, since the UE may not move directly between these two RA/TA (location update procedure is bound to be incurred during moving), the necessary paging area of UE is just the registered area of the RAT network where the UE currently locates. Therefore, the network side may page UE in an unnecessary paging area, reducing efficiency for paging UE.
After ISR (Idle mode Signaling Reduction) is activated, the HSS may record entity information of two systems. That is, the HSS may record information of SGSN and MME with which the UE registers, i.e., dual registration. However, single registration refers to that the HSS may only record information of the entity in one system after ISR is activated (i.e., record the information of the entity with which UE initiates the update most recently). However, information of entities in other system with which the UE registers is stored in another system entity. If the UE first registers with the 2G/3G network first, then the HSS records information of SGSN with which the UE registers (a location update message is sent to HSS via SGSN). When UE moves to another RAT i.e. the SAE system and initiates a location update, the UE again registers with MME in the SAE system. The ISR is then activated. Also, the MME sends a location update to HSS. The HSS records the information of MME and deletes the information of SGSN. However, the information of SGSN is stored in the MME. The SGSN and the MME all record UE information. However, the HSS only saves entity information of one system.